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At 22:21 6/1/01 -0400, Ludwik wrote:
Imagine a glass micro-pipette whose inner diameter is two
microns; it is 9 cm long. At both ends it progressively
(over a distance of 3.5 cm) becomes a pipette whose inner
diameter is 50 microns. In other words a glass tube with
a very narrow central region.

An extremely short (tens of femto-seconds ?), and very
intense (3.9 nJ), pulse of laser light enters the tube as
highly monochromatic (about 840 nm). And what comes
out? Photons whose wavelengths have a continuous
distribution from about 400 nm to about 1500 nm.
Ludwik Kowalski

You will remember, I'm sure the famous conundrum posed on this list,
"What happens when a car, rolling uphill is arrested at the wheels
at the instant it is reversing direction?"
It took a little while for the recognition of the body shimmy that ensues.

This laser observation of Ludwik's brought the question to mind.

You could ask, " What happens to the frequency content of a single cycle
of pure sinusoidal form, if it begins at the zero crossing point, and ends
at the second zero crossing later?"
"Is it different from the frequency content of a single cycle of the same
sinusoidal shape, which begins and ends at a positive peak amplitude with
two zero crossings?"

...all of which is to remind one that sampling a few cycles of a pure
monotone leads to an impure spectrum.
In that particular case, all the harmonic contributions are at higher
frequencies, so what is to be made of the sub harmonic at 1500 nm from an
840 nm fundamental?

Perhaps we are to think of energy division to two photons? or perhaps a
more likely route is the variety of non linear effects to be obtained
from very high energy pulses in a susceptible medium, or perhaps a pebble
hitting a liberty bell?....

[This is offered as a divergent, unfocussed narrative that is known to make
some goal directed people uncomfortable <:)> ]

brian whatcott <> Altus OK